Lactic-acid base resin composition and molded articles made therefor

ABSTRACT

The present invention provides a lactic acid-based resin composition comprising a mixture of (A) a mixture of (a1) polylactic acid and (a2) an aliphatic polyester, and (B) an aliphatic block co-polyester having a polylactic acid segment and an aliphatic polyester segment, wherein the aliphatic block co-polyester (B): (1) contains a lactic acid component in an amount of from 20 to 80 wt % in terms of monomer, (2) has a weight average molecular weight of 1,000 or more and less than 60,000, and (3) has a weight average molecular weight of the polylactic acid segment of from 500 to 55,000 and a weight average molecular weight of the aliphatic polyester segment of from 500 to 55,000. The lactic acid-based resin composition of the invention has transparency and flexibility because the respective compositional resins are effectively dispersed. The molded article formed therefrom is good in molding property, and in particular, a molded article thus stretched, oriented and crystallized, such as a film, a sheet, a filament and the like, has excellent mechanical property and heat resistance in addition to the foregoing properties.

TECHNICAL FIELD

[0001] The present invention relates to a lactic acid-based resincomposition and a molded article thereof. More specifically, it relatesto a lactic acid-based resin composition that is excellent inmoldability, flexibility and safety and is easily decomposed in thenatural environment after use, and a molded article thereof.

BACKGROUND ART

[0002] In general, as resins that are excellent in flexibility, heatresistance and water resistance, such resins are exemplified, aspolyethylene, polypropylene, plasticized polyvinyl chloride,polyethylene terephthalate and the like, and are used as a disposal bag,a packaging bag and the like. However, these resins increase the amountof waste upon discarding after use, and because they are substantiallynot decomposed under the natural environment, they semipermanentlyremain underground even when they are discarded underground. There alsoarise problems in that discarded plastics impair scenery and destroy thelife environments of marine organisms.

[0003] In order to cope therewith, as a polymer having biodegradability,which is a thermoplastic resin, an aliphatic polyester derived from apolyhydroxycarboxylic acid, such as polylactic acid and the like, withan aliphatic polyhydric alcohol and an aliphatic polyhydric carboxylicacid, and the like are being developed.

[0004] These polymers are completely decomposed in the body of animalswithin several months to one year, or when they are placed in earth orocean water, they begin to be decomposed within several weeks under awet environment and disappear within about one year to several years.Furthermore, they have such characteristics that the decomposed productsare lactic acid, carbon dioxide and water, which are harmless to humanbodies.

[0005] In particular, polylactic acid is expected to have an expandedutility field owing to the facts that L-lactic acid as the raw materialcan be mass-produced at low cost by the fermentation process, and itexhibits a large decomposition rate in barnyard manure, and hasexcellent characteristics, such as the resistance to fungus, resistanceto odorization and coloring of foods, and the like.

[0006] However, polylactic acid has high rigidity and thus cannot besaid that it is a resin suitable for such purposes that requireflexibility, such as a film, a packaging material and the like.

[0007] In general, it has been known as a method for softening a resinthat a soft polymer is blended, but when a soft general-purpose resin,such as resins including polyethylene, polypropylene, polyvinyl chlorideor the like, is mixed with polylactic acid, it is impossible to developa lactic acid-based resin composition having biodegradability andflexibility, which is the object of the invention described later.Therefore, what can impart flexibility to polylactic acid throughpolymer blend is limited to soft biodegradable resins. As these resins,polybutylene succinate, polyethylene succinate, polyhydroxybutyric acid,polyhydroxyvaleric acid, polycaprolactone, a copolymer and a mixturethereof, and the like are exemplified, and they have been disclosed inJapanese Patent Laid-Open No. 245866/1996 and Japanese Patent Laid-OpenNo. 111107/1997.

[0008] However, these soft resins have poor compatibility withpolylactic acid, and there are several problems upon practical use forproducing a film, a filament and the like when it is simply melted andmixed. For example, upon molding a film and a filament, because they arenot sufficiently attain uniform mixing even when they are subjected toheat melting and kneading in an extruder to cause viscosity unevenness,unevenness in thickness of a film and unevenness in diameter of a threadoccur, and furthermore, breakage of a film and breakage of a threadoccur, whereby stable molding is difficult to be carried out.

[0009] Moreover, even though a film or a thread can be obtained, uponsubsequently subjecting orientation by stretching for increasingproperties, such as heat resistance, strength and the like, it is liableto be broken upon stretching, whereby stable stretching cannot becarried out, or stretching cannot be carried out with sufficientmagnification. As a result, the heat resistance and the strength cannotbe sufficiently improved, and such a problem is caused in that a filmand a thread that can be practically used cannot be obtained.

[0010] Japanese Patent Laid-Open No. 262474/1998 discloses anagricultural sheet formed with a mixture of (A) crystalline polylacticacid having a melting point of 150° C. or more, (B) an aliphaticpolyester having a melting point of 140° C. or less formed with a lineardiol and an aliphatic dicarboxylic acid as main components, and (C) ablock copolymer of the polylactic acid (A) and the aliphatic polyester(B), and fibers. It is also disclosed that the mixture is improved inflowability and moldability in comparison to a simple mixture of thepolylactic acid and the aliphatic polyester of a linear diol and analiphatic dicarboxylic acid. However, there is no specific disclosure ofexamples, and in particular, it is expected from the description ofother examples that the block copolymer (C) has a molecular weight ofseveral hundreds of thousands. However, in the case where a blockpolymer having such a large molecular weight is used, the effects ofimprovement in flowability and moldability are not sufficiently exertedas is clear from the comparative examples described later.

[0011] As has been described, it is the current situation that it issubstantially difficult that a molded article, such as a film, afilament and the like, imparted with flexibility is stably obtained withgood productivity only by blending a soft biodegradable resin withpolylactic acid, and furthermore, it is substantially impossible withthe conventional techniques to improve properties, such as heatresistance, strength and the like, by orientation and crystallization bystretching.

[0012] In the invention, 1) a technique for effectively dispersing asoft biodegradable resin with polylactic acid, 2) development of aflexible lactic acid-based resin composition, and 3) a molded article,such as a film, a filament and the like, obtained from a flexible lacticacid-based resin composition, as well as 4) development of a productionprocess of a molded article that is highly and effectively imparted withpractical properties, such as strength, heat resistance, flexibility andthe like, from polylactic acid are designated as objects.

DISCLOSURE OF THE INVENTION

[0013] In order to attain the objects, the inventors have designed andexplored a compound for improving the compatibility between polylacticacid and a soft biodegradable resin, and as a result, such a compoundhas been found that has a sufficient compatibility effect with a smallamount to satisfy the objects, whereby the invention has been completed.

[0014] That is, the invention is identified by the following items [1]to [12].

[0015] [1] A lactic acid-based resin composition comprising a mixture ofa mixture (A) of polylactic acid (a1) and an aliphatic polyester (a2),and an aliphatic block co-polyester (B) having a polylactic acid segmentand an aliphatic polyester segment, wherein the aliphatic blockco-polyester (B) satisfies all the following conditions (1) to (3):

[0016] (1) it contains a lactic acid component in an amount -of from 20to 80 wt % in terms of monomer,

[0017] (2) it has a weight average molecular weight of 1,000 or more andless than 60,000, and

[0018] (3) it has a weight average molecular weight of the polylacticacid segment of from 500 to 55, 000 and a weight average molecularweight of the aliphatic polyester segment of from 500 to 55,000.

[0019] [2] A lactic acid-based resin composition described in item [1],wherein a compositional ratio of the mixture (A) and the aliphatic blockco-polyester (B) is from 0.05 to 10 parts by weight of the aliphaticblock co-polyester (B) per 100 parts by weight of the mixture (A).

[0020] [3] A lactic acid-based resin composition described in item [1]or [2], wherein the aliphatic polyester (a2) has an elastic modulusmeasured by the test method of JIS K6732 of 2,500 MPa or less.

[0021] [4] A lactic acid-based resin composition described anyone ofitems [1] to [3], wherein the mixture (A) of the polylactic acid (a1)and the aliphatic polyester (a2) has a mixing ratio of from 80 to 20parts by weight of the aliphatic polyester (a2) per from 20 to 80 partsby weight of the polylactic acid (a1).

[0022] [5] A lactic acid-based resin composition described anyone ofitems [1] to [4], wherein the aliphatic polyester (a2) is polybutylenesuccinate and/or polycaprolactone.

[0023] [6] A molded article comprising a lactic acid-based resincomposition described in anyone of items [1] to [5].

[0024] [7] A molded article described in item [6], which is stretched inat least one direction by from 1.1 to 15 times.

[0025] [8] A molded article described in item [6] or [7], wherein themolded article is a film or a sheet.

[0026] [9] A molded article described in item [6] or [7], wherein themolded article is a tape yarn.

[0027] [10] A molded article described in item [6] or [7], wherein themolded article is a mono-filament or multi-filaments.

[0028] [11] A molded article described in item [6] or [7], wherein themolded article is a nonwoven fabric.

[0029] [12] A process of using an aliphatic block co-polyester (B)having a polylactic acid segment and an aliphatic polyester segment, asa compatibility agent for a mixture (A) of polylactic acid (a1) and analiphatic polyester (a2), wherein the aliphatic block co-polyester (B)satisfies all the following conditions (1) to (3):

[0030] (1) it contains a lactic acid component in an amount of from 20to 80 wt % in terms of monomer,

[0031] (2) it has a weight average molecular weight of 1,000 or more andless than 60,000, and

[0032] (3) it has a weight average molecular weight of the polylacticacid segment of from 500 to 55, 000 and a weight average molecularweight of the aliphatic polyester segment of from 500 to 55,000.

BEST EMBODIMENT FOR CARRYING OUT THE INVENTION

[0033] The invention will be described in detail below.

[0034] In the invention, the mixture (A) of (a1) polylactic acid and(a2) an aliphatic polyester contains from 20 to 80 parts by weight ofthe polylactic acid (a1) and from 80 to 20 parts by weight of thealiphatic polyester (a2).

[0035] [Polylactic Acid (a1)]

[0036] As lactic acid used as a raw material of the polylactic acid,L-lactic acid, D-lactic acid, DL-lactic acid, a mixture thereof, andlactide, which is a cyclic dimer of lactic acid, can be exemplified.

[0037] As specific examples of a production process of the polylacticacid used in the invention, for example,

[0038] 1) a method using lactic acid as a raw material, which isdirectly subjected to dehydration polycondensation (for example, theproduction method shown in U.S. Pat. No. 5,310,865),

[0039] 2) a ring opening polymerization method, in which a cyclic dimerof lactic acid (lactide) is subjected to melt polymerization (forexample, the production method disclosed in U.S. Pat. No. 2,758,987),

[0040] 3) a method, in which upon producing a polyester polymer bycarrying out a dehydration polycondensation reaction of lactic acid inthe presence of a catalyst, solid phase polymerization is carried out inat least part of the process,

[0041] and the like can be exemplified, but it is not particularlylimited in the production process thereof. A small amount of analiphatic polyhydric alcohol, such as trimethylolpropane, glycerin andthe like, an aliphatic polybasic acid, such as butanetetracarboxylicacid and the like, and a polyhydric alcohol, such as a polysaccharide,may be copolymerized by coexisting, and the molecular weight may beincreased by using a binder (a polymer chain extending agent), such as adiisocyanate compound and the like.

[0042] [Aliphatic Polyester (a2)]

[0043] The soft aliphatic polyester (a2) used in the invention is apolymer having biodegradability that can be produced by variouslycombining the aliphatic hydroxycarboxylic acid, the aliphatic dihydricalcohol and the aliphatic dibasic acid described later, and preferablyhas an elastic modulus measured by the test method of JIS K6732 of 2,500MPa or less, more preferably from 1 to 1,500 MPa, further preferablyfrom 5 to 1,000 MPa, still further preferably from 5 to 750 MPa, andmost preferably from 5 to 500 MPa. When the elastic modulus is largerthan 2,500 MPa, the softening effect upon mixing with the polylacticacid is small.

[0044] As a preferred soft aliphatic polyester shown in the invention,for example, polyethylene succinate, polybutylene succinate,polybutylene succinate adipate, polyhydroxybutyric acid,polyhydroxyvaleric acid, a copolymer of β-hydroxybutyric acid andβ-hydroxyvaleric acid, polycaprolactone and the like can be exemplified.In particular, polybutylene succinate, polybutylene succinate adipateand polycaprolactone are preferred from the standpoint of the elasticmodulus and the easy availability with low cost.

[0045] The aliphatic polyester may be those having a polymer chainextended with a binder, such as a diisocyanate and the like, may bethose copolymerized in the presence of a small amount of an aliphaticpolyhydric alcohol, such as trimethylolpropane, glycerin and the like,an aliphatic polybasic acid, such as butanetetracarboxylic acid, or apolyhydric alcohol, such as polysaccharide, and further may be thosecrosslinked with an electron beam.

[0046] As a production method of the aliphatic polyester, the similarmethod as the production method of the polylactic acid may be used, andthe method is not limited.

[0047] [Aliphatic Hydroxycarboxylic Acid]

[0048] As specific examples of the aliphatic hydroxycarboxylic acid usedin the soft aliphatic polyester in the invention, glycolic acid, lacticacid, 3-hydroxybutyric acid, 4-hydroxybutyric acid, 3-hydroxyvalericacid, 4-hydroxyvaleric acid, 6-hydroxycaproic acid and the like can beexemplified, and furthermore, acyclic ester of the aliphatichydroxycarboxylic acid, such as glycolide, which is a dimer of glycolicacid, and ε-caprolactone, which is a cyclic ester of 6-hydroxycaproicacid, can be exemplified. These may be used solely or in combination oftwo or more of them.

[0049] Specific examples of the aliphatic dihydric alcohol used in thealiphatic polyester in the invention, for example, ethylene glycol,diethylene glycol, triethylene glycol, polyethylene glycol, propyleneglycol, dipropylene glycol, 1,3-butanediol, 1,4-butanediol,3-methyl-1,5-pentanediol, 1,6-hexanediol, 1,9-nonanediol, neopentylglycol, polytetramethylene glycol, 1,4-cyclohexanedimethanol and thelike can be exemplified. These may be used solely or in combination oftwo or more of them.

[0050] [Aliphatic Dibasic Acid]

[0051] Specific examples of the aliphatic dibasic acid used in the softaliphatic polyester in the invention, oxalic acid, glutaric acid, adipicacid, pimelic acid, suberic acid, azelaic acid, sebacic acid, undecanediacid, dodecane diacid, phenylsuccinic acid and the like can beexemplified. These may be used solely or in combination of two or moreof them.

[0052] [Molecular Weight of Polylactic Acid (a1) and Aliphatic Polyester(a2)]

[0053] The weight average molecular weights (Mw) and the molecularweight distributions of the polylactic acid (a1) and the aliphaticpolyester (a2) are not particularly limited as far as moldingfabrication can be substantially possible. The weight average molecularweights of the polylactic acid (a1) and the aliphatic polyester (a2)used in the invention are not particularly limited as far as theyexhibit substantially sufficient mechanical properties, and in general,it is preferably, in terms of weight average molecular weight (Mw), from60,000 to 1,000,000 , more preferably from 80,000 to 500,000, and mostpreferably from 100,000 to 300,000. In general, when the weight averagemolecular weight (Mw) is less than 60,000, a molded article obtained bymolding fabrication of the resin composition has insufficient mechanicalproperties, and when the molecular weight exceeds 1,000,000, there aresome cases where the melt viscosity upon molding fabrication becomesextremely high to make handling difficult, and the production becomesuneconomical.

[0054] [Aliphatic Block Co-polyester (B)]

[0055] The aliphatic block co-polyester (B) used in the invention is ablock copolymer formed with lactic acid with the aliphatic dibasic acid,the aliphatic dihydric alcohol and the aliphatic hydroxycarboxylic acid,and is a block copolymer containing from 20 to 80 wt % of a lactic acidcomponent in terms of monomer.

[0056] As the production process of the aliphatic block co-polyester (B)relating to the invention, it can be produced, for example, by applyingthe method of directly subjecting lactic acid to dehydrationpolycondensation and the method of ring opening polymerization oflactide, which is a dimer of lactic acid, which appear in the examplesfor polylactic acid described in the foregoing, and for example,

[0057] 1) a method, in which a monomer is subjected to ring openingpolymerization to form a polymer, and then other monomer component isadded to the polymer by ring opening polymerization, where one of themonomers is lactide, and

[0058] 2) a method, in which a polylactic acid component directlyobtained by dehydration polycondensation or ring opening polymerizationand an aliphatic polyester component obtained by the similar method aremixed and subjected to dehydration polycondensation addition in thepresence or absence of a catalyst and/or an organic solvent can beexemplified.

[0059] More specifically,

[0060] 1) a method as shown in Production Example 5-1, in whichcaprolactone is once subjected to ring opening polymerization in thepresence of a catalyst and an aliphatic alcohol to obtain the polymer,and then polymerization is carried out with lactide charged (two-stepring opening polymerization), and

[0061] 2) a method as shown in Production Example 5-10, in whichpolylactic acid, which is once directly obtained by dehydrationpolycondensation, and the other aliphatic polyester are mixed andsubjected to dehydration polycondensation in the presence of a catalystand an organic solvent (two-step dehydration polycondensation) can beexemplified.

[0062] In the invention, it is necessary that the molecular weight andthe molecular weights of the respective block units of the aliphaticblock co-polyester (B) are controlled to the particular ranges. As amethod therefor, a method, in which the reaction conditions, such as thereaction temperature, the time and the like upon polymerization, areappropriately changed to follow up progress of the polymerizationdegree, and a method of adding an end termination agent can beexemplified, and particularly, in the case of the ring openingpolymerization, the method of adding an end termination agent isparticularly preferred owing to the large polymerization rate.

[0063] As the end termination agent that can be used in the invention, acompound having a hydroxyl group or a carboxyl group, for example, acompound having a monofunctional group, such as an aliphatic alcohol, analiphatic carboxylic acid and an anhydride thereof, are preferred.

[0064] As the aliphatic alcohol, for example, a saturated orunsaturated, and linear or branched aliphatic alcohol having from 1 to30 carbon atoms is exemplified, and methanol, ethanol, propanol,iso-propanol, butanol, iso-butanol, hexanol, octanol, lauryl alcohol,palmityl alcohol, myristyl alcohol, stearyl alcohol, oleyl alcohol andthe like are exemplified.

[0065] As the aliphatic carboxylic acid and an anhydride thereof, forexample, a saturated or unsaturated, and linear or branched aliphaticcarboxylic acid having from 1 to 30 carbon atoms is exemplified, andacetic acid, propanoic acid, iso-propanoic acid, butanoic acid,iso-butanoic acid, tert-butanoic acid, heptanoic acid, iso-heptanoicacid, pentanoic acid, octanoic acid, lauric acid, palmitic acid, stearicacid, oleic acid, erucic acid, and behenic acid are exemplified. As theend termination agent used in the invention, ethanol, lauryl alcohol,palmityl alcohol, myrystyl alcohol, stearyl alcohol and oleyl alcoholare particularly preferably used.

[0066] The addition amount of the end termination agent is suitably from0.05 to 5 mol % based on the total molar number of the monomer unitsconstituting the aliphatic block co-polyester, preferably from 0.1 to 3mol %, and more preferably from 0.2 to 2 mol %. When it is less than0.05 mol %, the molecular weight of the aliphatic block co-polyesterbecomes large, and as a result, there are some cases where thecompatibility effect is not exerted. On the other hand, when it is morethan 5 mol %, the molecular weight of the aliphatic block co-polyesterbecomes small, and there are some cases where not only the compatibilityeffect is not exerted when formed into the composition of the invention,but also the mechanical strength is lowered.

[0067] The molecular weight of the aliphatic block co-polyester (B) isparticularly important, and is 1,000 or more and less than 60,000 interms of weight average molecular weight, preferably from 1,000 to50,000, more preferably from 3,000 to 40,000, and further preferablyfrom 5,000 to 30,000. When it is less than 1,000, the effect as thecompatibility agent disappears. When it is larger than 60,000, on theother hand, the effect of addition is not exerted.

[0068] The repeating unit of lactic acid, which is the essentialcomponent of the block copolymer, suitably has a weight averagemolecular weight of from 500 to 55,000, preferably from 1,500 to 50,000,more preferably from 3,000 to 40,000, and further preferably from 5,000to 30,000.

[0069] The other repeating unit of the aliphatic polyester suitably hasa weight average molecular weight of from 500 to 55,000, preferably from1,500 to 50,000, more preferably from 3,000 to 40,000, and furtherpreferably from 5,000 to 30,000.

[0070] [Addition Amount of Aliphatic Block Co-Polyester (B)]

[0071] The addition amount of the aliphatic block co-polyester (B) isfrom 0.05 to 10 parts by weight per 100 parts by weight of the mixture(A) of the polylactic acid (a1) and the other aliphatic polyester (a2).It is preferably from 0.1 to 7 parts by weight, more preferably from 0.2to 5 parts by weight, and further preferably from 0.3 to 3 parts byweight.

[0072] When the addition amount of the aliphatic block co-polyester (B)is less than 0.05 part by weight, there are some cases where thecompatibility effect is insufficient. When it exceeds 10 parts byweight, there are some cases where the heat resistance of the lacticacid-based resin composition is lowered, and the strength of theresulting molded article is decreased because the melting point and themolecular weight of the aliphatic block co-polyester (B) are relativelysmall.

[0073] The aliphatic block co-polyester (B) of the invention exhibits anexcellent compatibility effect when the polylactic acid (a1) and thealiphatic polyester (a2) are mixed. For example, when pellets obtainedby simply melting and kneading a mixture of polylactic acid andpolybutylene succinate are melted by heat and then cooled, an exothermicpeak due to crystallization of the polybutylene succinate component isobserved on thermal analysis with DSC, and by adding the aliphatic blockco-polyester (B) of the invention to the mixture, the exothermic peakdisappears. In other words, it is considered that the addition of thealiphatic block co-polyester (B) of the invention suppresses separationand rearrangement of the polybutylene succinate component in the mixtureupon melting and cooling to delay crystallization of the polybutylenesuccinate component, whereby the excellent compatibility effect isobtained. As a result, in a molded article formed by injection moldingor the like, since the polybutylene succinate component is effectivelydispersed in the mixture, the resulting molded article can exert a highelongation rate even when a relatively small amount of the aliphaticblock co-polyester (B) is added. In a molded article having beenstretched and oriented, such as a yarn, a filament, a nonwoven fabricand the like, concentration unevenness of the respective component andthickness unevenness in a molded article before stretching are decreasedby adding the aliphatic block co-polyester (B), and thus further uniformand high stretching becomes possible to obtain a molded article havinghigh strength.

[0074] [Other Additives]

[0075] In the lactic acid-based resin composition of the invention,various kinds of additives (a plasticizer, an antioxidant, anultraviolet ray absorbent, a heat stabilizer, a flame-retardant, aninternal releasing agent, an inorganic additive, an antistatic agent, asurface wettability improving agent, a combustion assistant, a pigment,a lubricant and a natural matter) and the like may be addedcorresponding to the objects (for example, improvement in moldability,secondary workability, degradability, tensile strength, heat resistance,storage stability, weather resistance and the like).

[0076] For example, in inflation molding and T-die extrusion molding, aninorganic additive and a lubricant (an aliphatic carboxylicamide, analiphatic carboxylic bisamide and the like) may be added for blockingprevention and improvement of sliding property of a film and a sheet.

[0077] As the inorganic additive, silica, calcium carbonate, talc,kaolin, kaolinite, carbon, titanium oxide, zinc oxide and the like areexemplified, and in particular, silica and calcium carbonate arepreferred. These may be used solely or as a mixture of two or more ofthem.

[0078] As the organic additive, starch and a derivative thereof,cellulose and a derivative thereof, pulp and a derivative thereof, paperand a derivative thereof, flour, bean curd refuse, palm chaff, coffeesullage, protein and the like are exemplified. These may be used solelyor as a mixture of two or more of them.

[0079] [Production Process of Lactic Acid-Based Resin Composition]

[0080] The lactic acid-based resin composition of the invention isobtained by mixing and kneading the polylactic acid (a1) with the otheraliphatic polyester (a2) and the aliphatic block co-polyester (B), aswell as, depending on necessity, other additives. While the method formixing and kneading is not particularly limited, a method, in whichafter uniformly mixing by using a high-speed mixer or a low-speed mixer,melt kneading is carried out with a mono-axial or multi-axial extruderhaving sufficient kneading performance, and a method of mixing andkneading upon melting can be employed.

[0081] In general, the shape of the lactic acid-based resin compositionrelating to the invention is preferably pellets, bars, powder and thelike.

[0082] [Molded Article and Production Process Thereof]

[0083] The lactic acid-based resin composition of the invention is apreferred material that can be applied to the known molding methods, andas the resulting molded article, while not limited, for example, a film,a sheet, a mono-filament, multi-filaments, such as fibers, a nonwovenfabric and the like, an injection-molded article, a blow-molded article,a laminated article, a foamed article, a heat-molded article, such asvacuum-molded article and the like.

[0084] The lactic acid-based resin composition of the invention is goodin molding property upon orientation and crystallization by stretching,and because the effect of the invention is markedly exhibited thereupon,it is preferred for the production of a film, a sheet, a tape yarn, astretched blow-molded product, mono- and multi-filaments and a nonwovenfabric that are obtained by stretching.

[0085] As a molding method of the molded article obtained from thelactic acid-based resin composition of the invention, an injectionmolding method, a blow molding method (injection stretching blow,extrusion stretching blow and direct blow), a balloon method, aninflation method, a co-extrusion method, a calender method, a hot pressmethod, a solvent casting method, a (stretching) extrusion method, anextrusion lamination method with paper or aluminum, contour extrusionmolding, thermoforming such as vacuum (pressure) forming, melt spinning(a mono-filament, multi-filaments, a spun-bonding method, a melt-blownmethod, a fibrillated film yarn method and the like), a foaming moldingmethod, a compression molding method and the like can be exemplified,and it can be applied to any method.

[0086] In particular, in the case of a molding method, such as extrusionmolding, melt spinning and the like, containing steps of orientation andcrystallization, the practical strength and the appearance, such asstrength, heat resistance, impact resistance, transparency and the like,of the resulting molded article can be improved, and thus is can be morepreferably used.

[0087] The molded article obtained by the lactic acid-based resincomposition of the invention encompasses molded articles obtained by theknown molding methods, and the shape, the size, the thickness, thedesign and the like thereof are not limited.

[0088] [Specific Examples of Purpose]

[0089] The molded article obtained by molding the lactic acid-basedresin composition of the invention by using the foregoing moldingmethods can be preferably used as materials for wide ranges includingvarious kinds of wrapping films for foods, electronics, medical use,pharmaceuticals, cosmetics and the like, and materials used in thefields of agriculture, civil engineering and fishery, for example, abottle, a film or a sheet, a hollow tube, a laminated article, a vacuum(pneumatic) molded article, mono- or multi-filaments, a nonwoven fabric,a foamed article, a shopping bag, a paper bag, a shrink film, a disposalbag, a compost bag, a lunch box, a bag for prepared foods, a packagingfilm for foods and confections, a wrapping film for foods, a wrappingfilm for cosmetics and perfumes, a diaper, a sanitary napkin, a wrappingfilm for pharmaceuticals, a wrapping film for a surgical patch drugapplied to stiff neck, sprain and the like, a film for agriculture andhorticulture, a wrapping film for agricultural chemicals, a film forgreen houses, a bag for manure, a packaging band, a packaging film for amagnetic tape cassette, such as those for video, audio and the like, awrapping form for floppy disks, a film for prepress, an adhesive tape, atape, a yarn, a pot for raising of seedling, a waterproof sheet, a soilbag, a building film, a weed-control sheet, a vegetation net and thelike.

EXAMPLE

[0090] The invention will be specifically described with reference tothe examples below, but it is not limited thereto unless it exceeds thetechnical range of the invention.

[0091] The weight average molecular weight (Mw), the physical propertiesand the like shown in Production Examples, Examples and ComparativeExamples were measured in the manners shown below.

[0092] 1) Weight Average Molecular Weight (Mw)

[0093] It was measured by gal permeation chromatography (GPC) by thepolystyrene standard at a column temperature of 40° C. with chloroformas a solvent.

[0094] 2) Strength, Elastic Modulus (Flexibility) and Elongation Rate ofFilm

[0095] They were obtained according to JIS K6732. The flexible filmdefined in the invention has an elastic modulus in a range of 2,500 MPa.

[0096] 3) Tensile Strength, Elongation Rate, Flexural Strength andFlexural Elastic Modulus of Dumbbell Piece

[0097] A test piece obtained by injection molding was evaluatedaccording to ASTM D-790.

[0098] 4) Strength and Elongation Rate of Filament

[0099] They were obtained according to JIS L1095.

[0100] 5) Folding Endurance

[0101] It was obtained according to JIS P8115.

[0102] 6) Haze

[0103] It has measured according to JIS K-6714 by using Haze Meterproduced by Tokyo Denshoku Co., Ltd.

[0104] 7) Dropping Impact Test

[0105] 800 ml of water was charged in a 1,000 ml-container, which wasdropped on a concrete floor from a height of 1.5 m under the conditionof an atmospheric temperature of 20° C., so as to obtain the number oftimes until the container was broken. The number of times of droppingwas repeated until ten times.

Production Example 1 (Production of Polylactic Acid)

[0106] 400 kg of L-lactide, 0.04 kg of stannous octanoate and 0.12 kg oflauryl alcohol were charged in a cylindrical stainless steel-madepolymerization container with large thickness having an agitator, anddeaerated for 2 hours. After substituting with a nitrogen gas, they wereheated and agitated at 200° C. and 10 mmHg for 2 hours.

[0107] After completing the reaction, a molten matter of polylactic acidwas taken out from an outlet at an lower part, and then it was cooledand cut by a pelletizer. The resulting polylactic acid exhibited anyield amount of 340 kg, an yield of 85% and a weight average molecularweight (Mw) of 138,000.

Production Example 2 (Production of Polylactic Acid)

[0108] 100 kg of 90% L-lactic acid and 450 g of tin powder were chargedin a reactor having a Dien-Stark trap, and water was distilled off at150° C. and 50 mmHg for 3 hours under agitation, followed by furtheragitating for 2 hours at 150° C. and 30 mmHg, so as to form an oligomer.210 kg of diphenyl ether was added to the oligomer, and an azeotropicdehydration reaction was carried out at 150° C. and 35 mmHg. Water andthe solvent thus distilled off were separated by a water separator, andonly the solvent was returned to the reactor. After lapsing 2 hours, theorganic solvent to be returned to the reactor was returned to thereactor after passing through a column filled with 46 kg of molecularsieve 3A, and the reaction was carried out at 130° C. and 17 mmHg for 20hours, so as to obtain a polylactic acid solution having a weightaverage molecular weight (Mw) of 150,000. After diluting the solution byadding 440 kg of dehydrated diphenyl ether thereto, it was cooled to 40°C., and crystals thus deposited were filtered off. 120 kg of 0.5 N HCland 120 kg of ethanol were added to the crystals, which was thenagitated at 35° C. for 1 hour, followed by filtering and drying at 60°C. and 50 mmHg, so as to obtain 61 kg of polylactic acid powder (yield:85%).

[0109] The powder was pelletized by melting in an extruder to obtainpellets of polylactic acid. The polymer had a weight average molecularweight (Mw) of 147,000.

Production Example 3 (Production of Polybutylene Succinate)

[0110] 293.0 kg of diphenyl ether and 2.02 kg of metallic tin were addedto 50.5 kg of 1,4-butanediol and 66.5 kg of succinic acid, and heatedand agitated at 130° C. and 140 mmHg for 7 hours with distilling offwater to form an oligomer. A Dien-Stark trap was attached thereto, andazeotropic dehydration was carried out at 140° C. and 30 mmHg for 8hours. Thereafter, a tube filled with 40 kg of molecular sieve 3A wasattached so that the distilled solvent was passed through the molecularsieve tube and was returned to the reactor, followed by agitating at130° C. and 17 mmHg for 49 hours. The reaction mass was dissolved in 600L of chloroform and was added to 4 kL of acetone to effectreprecipitation, and then sludging was carried out with an isopropylalcohol (hereinafter abbreviated as IPA) solution of HCl (HClconcentration: 0.7 wt %) for 0.5 hour, followed by filtering. Afterwashing the resulting cake with IPA, it was dried under reduced pressureat 60° C. for 6 hours, so as to obtain polybutylene succinate(hereinafter abbreviated as PSB). The polymer had a molecular weight of140,000 and exhibited an yield of 92%.

Production Example 4 (Production of Polyhydroxycaproic Acid)

[0111] A reaction was carried out in the same manner as in ProductionExample 2 except that 6-hydroxycaproic acid was used instead of lacticacid, and as a result, polyhydroxycaproic acid (weight average molecularweight (Mw): 150,000, yield: 90%) was obtained.

Production Example 5 (Production of Aliphatic Block Co-Polyester (B))Production Example 5-1 (Production of Block Copolymer ofPolycaprolactone and Polylactic Acid)

[0112] 80 g of caprolactone, 1.6 g of ethanol and 0.56 g of tin (II)laurate were charged in a 1-L autoclave, and after sufficientlyreplacing the interior of the reactor with nitrogen, they were heated toa temperature of from 90 to 100° C. for 8 hours to obtainpolycaprolactone (PCL) having a weight average molecular weight (Mw) of8,000.

[0113] After charging 101 g of lactide, 0.56 g of tin (II) laurate and20 g of toluene in the autoclave, the interior of the reaction systemwas replaced with nitrogen, and was heated to a temperature of from 100to 110° C. for further 8 hours. The reaction mass inside the reactor wasprogressively solidified to be a block form.

[0114] After completing the reaction and cooling, 400 ml of chloroformwas added to the reaction mass for dissolution, and it was addeddropwise to 4 L of agitated methanol to deposit a polymer, which wasthen filtered off, followed by washing with hexane and drying.

[0115] The resulting polymer was a block copolymer of polycaprolactone(PCL) and polylactic acid (PLA) having a weight average molecular weightof 23,000 and exhibited an yield of 92%. The differential scanningcaloric analysis (DSC analysis) of the block copolymer demonstratedmelting points ascribed to the PCL segments and the PLA segments.

Production Example 5-2 (Production of Random Polymer of Caprolactone andLactic Acid)

[0116] The same procedures were carried out as in Production Example 5-1except that the raw materials were charged all together, and as aresult, a random copolymer of caprolactone and lactic acid was obtained.The yield was 87%, and the weight average molecular weight was 25,000.Melting points ascribed to the PCL block and the PLA block were notobserved in the DSC analysis of the polymer.

Production Example 5-3 to 5-8

[0117] The same procedures as in Production Example 5-1 were carried outexcept that the amounts of ethanol (EtOH) and lactide (LTD) werechanged. The results are shown in Table 1. TABLE 1 Production ExampleNo. 5-3 5-4 5-5 5-6 5-7 5-8 CL amount (g) 80 80 80 80 80 80 EtOH amount(g) 1.6 0.8 1.2 0.4 1.6 0.2 Mw of PCL  6,000 18,000 14,000 31,000  8,000 74,000 LTD amount (g) 100 100 100 101 300 100 Mw of block copolymer25,000 42,000 33,000 77,000 85,000 168,000

Production Example 5-9 (Production of Block Copolymer of PolybutyleneSuccinate and Polylactic Acid)

[0118] 293.0 g of diphenyl ether and 2.02 g of metallic tin were addedto 50.5 g of 1,4-butanediol and 66.5 g of succinic acid, and heated andagitated at 130° C. and 140 mmHg for 7 hours with distilling off waterto the outside of the system, so as to form an oligomer. The weightaverage molecular weight was 10, 000.

[0119] 50.0 g of polylactic acid (weight average molecular weight:8,600) obtained in the same manner as in Production Example 2 and 0.7 gof metallic tin were mixed with the resulting reaction mass ofpolybutylene succinate, and again subjected to a dehydrationpolycondensation reaction at 130° C. and 17 mmHg for 8 hours. Aftercompleting the reaction, the same post treatments were carried out inthe same manner as in Production Example 2 to obtain 89.7 g of a blockcopolymer of polybutylene succinate and polylactic acid. The blockcopolymer had a weight average molecular weight of 22,000.

Production Example 5-10 (Production of Block Copolymer ofPolyhydroxycaproic Acid and Polylactic Acid)

[0120] 100 g of 90% L-lactic acid and 450 mg of tin powder were chargedin a reactor having a Dien-Stark trap, and water was distilled off at150° C. and 35 mmHg for 3 hours under agitation, followed by furtheragitating for 2 hours at 150° C. and 30 mmHg, so as to form an oligomer.210 g of diphenyl ether was added to the oligomer, and an azeotropicdehydration reaction was carried out at 150° C. and 35 mmHg. Water andthe solvent thus distilled off were separated by a water separator, andonly the solvent was returned to the reactor. Polylactic acid in thereaction mass had a weight average molecular weight of 7, 500.

[0121] Separately, the formation of an oligomer and anazeotropicdehydration reaction were carried out in the same manner except that 100g of 6-hydroxylcarboxylic was used instead of 90% L-lactic acid, and asa result, a reaction mass of polyhydroxycaproic acid having a weightaverage molecular weight of 12,000 was obtained.

[0122] 150 g of the reaction mass of polylactic acid was charged in thereactor of 150 g of reaction mass of polyhydroxycaproic acid, and anazeotropic dehydration reaction was again carried out at 150° C. and 35mmHg for 4 hours. A block copolymer of polylactic acid andpolyhydroxycaproic acid in the reaction mass was obtained. The weightaverage molecular weight was 27,000.

[0123] After adding 440 g of dehydrated diphenyl ether to the solutionfor dilution, it was cooled to 40° C., and crystals thus deposited werefiltered off. 120 g of 0.5 N-HCl and 120 g of ethanol were added to thecrystals, which was then agitated at 35° C. for 1 hour, followed byfiltering and drying at 60° C. and 50 mmHg, so as to obtain a blockcopolymer with polyhydroxycaproic acid.

Example 1-1

[0124] 140 kg of the polylactic acid obtained in Production Example 1,60 kg of the polybutylene succinate obtained in Production Example 3,and 1 kg of the block co-polyester of polylactic acid andpolycaprolactone obtained in Production Example 5-1 were mixed in aHenschel mixer and then pelletized by a biaxial extruder under theconditions of a cylinder preset temperature of from 180 to 210° C. Afterdrying the pellets at 80° C. for 10 hours, spinning molding was carriedout at a temperature of from 200 to 220° C. by using a forming winder of65 mm (dice diameter: 40 mm, number of nozzles: 90) to obtain anon-stretched thread, which is then subjected to stretching in a firstwater bath at a temperature of from 70 to 80° C. and a second water bathat from 90 to 100° C. (total stretching ratio: 7.2 times), followed bysubjecting to a heat treatment through an atmosphere of from 100 to 120°C.

[0125] The spinning property was stable and good. The resulting threadhad a thread thickness of 500 d, a strength of 4.78±0.15 g/d, and anelongation rate of 22±3%. The results are shown in Table 2.

Examples 1-2 to 1-6

[0126] The same procedures as in Example 1-1 were carried out exceptthat instead of the block co-polyester of polylactic acid andpolycaprolactone obtained in Production Example 5-1 used in Example 1-1,the block co-polyesters produced in the other production conditions wereused. The spinning properties, the stretching ratios and the propertiesof the resulting threads are shown in Table 2. TABLE 2 Example No. 1-11-2 1-3 1-4 1-5 1-6 Lactic acid-based resin composition Polylactic acid(a1) Production Production Production Production Production Productionkind Example 1 Example 2 Example 2 Example 2 Example 1 Example 1 amount(kg) 140 120 140 120 140 140 Aliphatic polyester (a2) ProductionProduction Production Production Production Production kind Example 3Example 3 Example 4 Example 4 Example 3 Example 4 amount (kg) 60 80 6060 60 60 Aliphatic block co-polyester (B) kind 5-1 5-3 5-4 5-5 5-9 5-10amount (kg) 1.0 1.5 2.0 1.0 2.0 1.5 Spinning property good good goodgood good good Stretching condition 7.2 7.6 7.5 8.0 7.2 7.5 Stretchingratio Properties of thread Thickness (d) 500 500 500 500 500 500Strength (g/d) 4.78 ± 0.15 4.11 ± 0.20 4.67 ± 0.18 4.01 ± 0.17 4.72 ±0.19 4.82 ± 0.16 Elongation rate (%)   22 ± 3     28 ± 4     24 ± 2    30 ± 4     22 ± 3     25 ± 2  

Comparative Example 1-1

[0127] The same procedures as in Example 1-1 were carried out exceptthat the addition of the block co-polyester used in Example 1-1 wasomitted. The spinning property was that thread breakage sometimesoccurred, and stable spinning could not be carried out. The stretchingratio was 5.8 times. The resulting thread had a thread thickness of 500d, a strength of 2.86±0.4 g/d, and an elongation rate of 25±6%. Theresults are shown in Table 3.

Comparative Examples 1-2 to 1-5

[0128] The same procedures as in Example 1-1 were carried out exceptthat instead of the block co-polyester used in Example 1-1, the otherblock co-polyesters were used. The spinning properties, the stretchingratios and the properties of the resulting threads are shown in Table 3.TABLE 3 Comparative Example No. 1-1 1-2 1-3 1-4 1-5 1-6 Lacticacid-based resin composition Polylactic acid (a1) Production ProductionProduction Production Production Production kind Example 1 Example 2Example 2 Example 2 Example 2 Example 2 amount (kg) 140 140 140 120 140140 Aliphatic polyester (a2) Production Production Production ProductionProduction Production kind Example 3 Example 3 Example 4 Example 4Example 4 Example 3 amount (kg) 60 60 60 60 60 60 Aliphatic blockco-polyester kind — 5-2 — 5-6 5-7 5-8 amount (kg) — 1.0 — 2.0 2.0 1.0Spinning property poor poor poor poor poor poor Stretching condition 5.86.2 6.1 6.5 6.3 6.4 Stretching ratio Properties of thread Thickness (d)500 500 500 500 500 500 Strength (g/d) 2.86 ± 0.4 2.43 ± 0.51 2.75 ±0.42 2.41 ± 0.45 2.85 ± 0.50 2.90 ± 0.43 Elongation rate (%)   25 ± 6    33 ± 6     24 ± 6     32 ± 6     22 ± 3     22 ± 3  

Example 2 (Injection Molding)

[0129] 0.5 part by weight of the block co-polyester obtained inProduction Example 5-10 was mixed with 60 parts by weight of thepolylactic acid obtained in Production Example 1 and 40 parts by weightof Celgreen PH-7 (a trade name, produced by Daicel Chemical Industries,Ltd.) as polycaprolactone, and it was pelletized at 190° C. by using abiaxial extruder. The resulting pellets were dried at 80° C. for 8hours. The pellets were subjected to injection molding to a metallicmold set at from 10 to 30° C. by using an injection molding machinehaving a dehumidifying dryer at a cylinder temperature of from 140 to220° C. and a dice temperature of from 170 to 190° C., so as to obtain amolded article of a dumbbell piece for tension and flexure. Theresulting dumbbell piece had a flexural strength of 65 MPa, a flexuralelastic modulus of 2,200 MPa, a tensile strength of 55 MPa and anelongation rate of 220%.

Comparative Example 2 (Injection Molding)

[0130] The same procedures as in Example 2 were carried out except thatthe block co-polyester was not used, and as a result, the resultingdumbbell piece had a flexural strength of 67 MPa, a flexural elasticmodulus of 2,300 MPa, a tensile strength of 57 MPa and an elongationrate of 25%.

Example 3 (Spinning Molding (Production of Multifilaments))

[0131] 0.5 part by weight of the block co-polyester obtained inProduction Example 5-1 was mixed with 70 parts by weight of thepolylactic acid obtained in Production Example 2 and 40 parts by weightof Bionolle 1001 (a trade name, produced by Showa Highpolymer Co., Ltd.)as polybutylene succinate, and it was pelletized at 190° C. by using abiaxial extruder. The resulting pellets were dried at 80° C. for 8hours.

[0132] The pellets were spun by using a dry spinning machine having adehumidifying dryer wit a dice having a pore diameter of 0.2 mm and anumber of pores of 20 at a temperature of 230° C. to obtain asemistretched thread. The molding property upon molding was thatspinning could be carried out in good conditions without threadbreakage.

[0133] The resulting thread was stretched at a temperature of from 80 to100° C. and subjected to thermal fixing at a temperature of from 120 to140° C.

[0134] The resulting fibers had a thread diameter of 5 d and a strengthof 4.85±0.17 g/d.

Comparative Example 3 (Spinning Molding (Production of Multifilaments))

[0135] The same procedures as in Example 3 were carried out except thatthe block co-polyester was not used to obtain pellets, and spinning wascarried out at a dice temperature of 230° C.

[0136] The molding property upon molding was that thread breakagesometimes occurred, and good spinning and stretching could not becarried out.

[0137] The resulting fibers had a thread diameter of 5 d and a strengthof 3.00±0.41 g/d.

Example 4 (Paper Lamination Molding)

[0138] 1.0 part by weight of the block co-polyester obtained in Example5-1 was mixed with 60 parts by weight of the polylactic acid obtained inProduction Example 2 and 40 parts by weight of the polybutylenesuccinate obtained in Production Example 3, and it was pelletized at190° C. by using a biaxial extruder. The resulting pellets were dried at90° C. for 8 hours.

[0139] The pellets were subjected to kneading and melting and wereextruded on kraft paper (basis weight: 75 g/m²) at a winding speed of120 m/min by using an extruder having a dehumidifying dryer with a T-diehaving a width of 1,300 mm and a lip width of 0.8 mm at 235° C.

[0140] The film forming property at this time was good with no filmbreakage.

[0141] The resulting paper laminated product had a thickness of theresin layer of 20±2 μm, and the thickness acuracy was good.

Comparative Example 4 (Paper Lamination Molding)

[0142] Pellets were obtained in the same manner as in Example 4 exceptthat the block co-polyester was not used, and were extruded at a dicetemperature of 235° C. The film forming property at this time was thatfilm breakage sometimes occurred, and stable molding could not becarried out. The resulting paper laminated product had a thickness ofthe resin layer of 23±7 μm, and the thickness acuracy was not very good.

Example 5 (Stretching Blow Molding)

[0143] 1.0 part by weight of the block co-polyester obtained inProduction Example 5-1 was mixed with 60 parts by weight of thepolylactic acid obtained in Production Example 2 and 40 parts by weightof the polybutylene succinate obtained in Production Example 3, and itwas pelletized at 190° C. by using a biaxial extruder, followed bydrying at 90° C. for 8 hours. By using the pellets, they were melted inan injection stretching blow molding machine at a cylinder temperatureof from 140 to 250° C. to effect injection molding to a metallic moldset at from 0 to 50° C., so as to obtain a cold parison in a weight of40 g. After heating and softening the resulting parison at 100° C., itwas moved to the interior of a metallic mold having a bottle shape, intowhich pressurized air at 1 MPa was blown to effect blow stretching at3.5 times in the vertical direction and 3 times in the horizontaldirection, whereby a cylindrical bottle having a bore diameter of 75 mm,a height of 100 mm and an internal volume of 1,000 ml was obtained. Thethickness of the wall was 0.2 mm, and the haze was 2.6%.

[0144] 800 ml of water was charged in the blown container, which wasrepeatedly dropped on a concrete floor from a height of 1.5 m 10 timesunder the condition of an atmospheric temperature of 20° C., but it wasnot broken.

Comparative Example 5 (Stretching Blow Molding)

[0145] The same procedures as in Example 5 were carried out to produce abottle having an internal volume of 1,000 ml except that the blockco-polyester was not used, and as a result, a cylindrical bottle havinga bore diameter of 75 mm, a height of 100 mm and an internal volume of1,000 ml was obtained. The thickness of the wall was 0.2 mm, and thehaze was 20%.

[0146] 800 ml of water was charged in the blown container, which wasrepeatedly dropped on a concrete floor from a height of 1.5 m under thecondition of an atmospheric temperature of 20° C., and it was broken atthe third drop.

Example 6 (Extrusion Stretching Molding)

[0147] 0.5 part by weight of the block co-polyester obtained inProduction Example 5-1 was mixed with 60 parts by weight of thepolylactic acid obtained in Production Example 1 and 40 parts by weightof the polybutylene succinate obtained in Production Example 3, and itwas pelletized at 190° C. by using a biaxial extruder. The resultingpellets were dried at 80° C. for 8 hours. By using the resultingpellets, they were formed into a film having a thickness of 200 μm byusing an extruder having a dehumidifying dryer. The film was stretched2.5 times in the vertical direction and 2.5 times in the horizontaldirection in an oven set at a temperature of from 65 to 75° C.

[0148] The resulting film had a thickness of 30 μm, a tensile strengthof 45 MPa, a tensile elastic modulus of 1,200 MPa, an elongation rate of300%, a haze of 2.3%, and a folding endurance of 5,000 times or more.

Comparative Example 6 (Extrusion Stretching Molding)

[0149] The same procedures as in Example 6 were carried out except thatthe block co-polyester was not used, and as a result, a film having athickness of 200 μm was obtained. The film was stretched 2.5 times inthe vertical direction and 2.5 times in the horizontal direction in anoven set at a temperature of from 65 to 75° C.

[0150] The resulting film had a thickness of 30 μm, a tensile strengthof 43 MPa, a tensile elastic modulus of 1,300 MPa, an elongation rate offrom 20 to 280%, a haze of 6.1%, and a folding endurance of from 1,500to 5,000 times.

Example 7 (Tape Yarn Molding)

[0151] 0.5 part by weight of the block co-polyester obtained inProduction Example 5-1 was mixed with 70 parts by weight of thepolylactic acid obtained in Production Example 1 and 30 parts by weightof the polybutylene succinate obtained in Production Example 3, and itwas pelletized at 190° C. by using a biaxial extruder. The resultingpellets were dried at 80° C. for 8 hours. By using the resultingpellets, they were formed into a film by using a 90 mm-extruder having adehumidifying dryer with a dice width of 1,200 mm and a lip gap of 0.8mm at a temperature of from 150 to 210° C., so as to obtain a filmhaving a thickness of 100 μm. The film was slit into a width of 6 mm andstretched 5 times by heat plate stretching at a temperature of from 65to 80° C., followed by thermal fixing on a heat plate at from 100 to120° C. The resulting tape had a width of 3.5 mm, a thickness of 30 μmand a strength of 5.10±0.13 g/d.

Comparative Example 7 (Tape Yarn Molding)

[0152] The same procedures as in Example 7 were carried out except thatthe block co-polyester was not used, and as a result, a tape having awidth of 3.6 mm and a thickness of 35 μm was obtained. The resultingtape had a strength of 2.89±0.47 g/d.

Example 8 (Nonwoven Fabric Molding)

[0153] 0.5 part by weight of the block co-polyester obtained inProduction Example 5-1 was mixed with 70 parts by weight of thepolylactic acid obtained in Production Example 2 and 30 parts by weightof the polybutylene succinate obtained in Production Example 3, and itwas pelletized at 190° C. by using a biaxial extruder. The resultingpellets were dried at 80° C. for 8 hours. The pellets were melted at210° C. and subjected to melt spinning through a spinning die havingspinning pores of a pore diameter of 0.35 mm, and they were picked up byan air sucker arranged under the surface of spinning die by 1,300 mm andwere accumulated on a moving collecting surface to form a web. Thepickup speed at this time was about 3,500 m/min.

[0154] The resulting web was passed between a metallic embossed rollheated to a temperature of from 80 to 100° C. and a smooth metallic rollheated to the same temperature as the metallic embossed roll to effectheat fusion, whereby a nonwoven fabric was obtained.

[0155] The short fiber strength of the resulting nonwoven fabric was 2.5d, and the basis weight of the nonwoven fabric was 30 g/m². The nonwovenfabric was treated in an oven at 90° C. for 60 seconds, and theshrinking degree obtained from the dimensions before and after thetreatment was 5.8%.

Comparative Example 8

[0156] Pellets were obtained in the same manner as in Example 8 exceptthat the block co-polyester was omitted, and they were subjected to meltspinning at 210° C.

[0157] The spinning property upon molding was that thread breakagesometimes occurred, and good spinning could not be carried out under theconditions of a pickup speed of about 3,500 m/min.

[0158] When the pickup speed was then decreased to about 2,600 m/min,spinning could be carried out without thread breakage to obtain anonwoven fabric having a short fiber strength of 3.0 d and a basisweight of 30 g/m², but the shrinking degree after treating in an oven at90° C. for 60 seconds was as large as 17%.

[0159] INDUSTRIAL AVAILABLENESS

[0160] The lactic acid-based resin composition relating to the inventionhas transparency and flexibility because the respective compositionalresins are effectively dispersed. The molded article formed therefrom isgood in molding property, and in particular, a molded article thusstretched, oriented and crystallized, such as a film, a sheet, afilament and the like, is a molded article that has excellent mechanicalproperty and heat resistance in addition to the foregoing properties.Therefore, it can be preferably used as materials of wide ranges, suchas various kinds of packaging materials for food, electronics, medicaluse, pharmaceuticals, cosmetics and the like, materials for agriculture,civil engineering and construction, and fishery, a compost material, andthe like. When it is discarded after use, it is not accumulated asindustrial waste and domestic waste.

1. A lactic acid-based resin composition comprising a mixture of amixture (A) of polylactic acid (a1) and an aliphatic polyester (a2), andan aliphatic block co-polyester (B) having a polylactic acid segment andan aliphatic polyester segment, wherein the aliphatic block co-polyester(B) satisfies all the following conditions (1) to (3): (1) it contains alactic acid component in an amount of from 20 to 80 wt % in terms ofmonomer, (2) it has a weight average molecular weight of 1,000 or moreand less than 60,000, and (3) it has a weight average molecular weightof the polylactic acid segment of from 500 to 55, 000 and a weightaverage molecular weight of the aliphatic polyester segment of from 500to 55,000.
 2. The lactic acid-based resin composition according to claim1, wherein a compositional ratio of the mixture (A) and the aliphaticblock co-polyester (B) is from 0.05 to 10 parts by weight of thealiphatic block co-polyester (B) per 100 parts by weight of the mixture(A).
 3. The lactic acid-based resin composition according to claim 1,wherein the aliphatic polyester (a2) has an elastic modulus measured bythe test method of JIS K6732 of 2, 500 MPa or less.
 4. The lacticacid-based resin composition according to claim 1, wherein the mixture(A) of the polylactic acid (a1) and the aliphatic polyester (a2) has amixing ratio of from 80 to 20 parts by weight of the aliphatic polyester(a2) per from 20 to 80 parts by weight of the polylactic acid (a1). 5.The lactic acid-based resin composition according to claim 1, whereinthe aliphatic polyester (a2) is polybutylene succinate and/orpolycaprolactone.
 6. A molded article comprising a lactic acid-basedresin composition according to claim
 1. 7. The molded article accordingto claim 6, which is stretched in at least one direction by from 1.1 to15 times.
 8. The molded article according to claim 6, wherein the moldedarticle is a film or a sheet.
 9. The molded article according to claim6, wherein the molded article is a tape yarn.
 10. The molded articleaccording to claim 6, wherein the molded article is a mono-filament ormulti-filaments.
 11. The molded article according to claim 6, whereinthe molded article is a nonwoven fabric.
 12. A process of using (B) analiphatic block co-polyester having a polylactic acid segment and analiphatic polyester segment, as a compatibility agent for a mixture (A)of polylactic acid (a1) and an aliphatic polyester (a2), wherein thealiphatic block co-polyester (B) satisfies all the following conditions(1) to (3): (1) it contains a lactic acid component in an amount of from20 to 80 wt % in terms of monomer, (2) it has a weight average molecularweight of 1,000 or more and less than 60,000, and (3) it has a weightaverage molecular weight of the polylactic acid segment of from 500 to55,000 and a weight average molecular weight of the aliphatic polyestersegment of from 500 to 55,000.